1. Field of the Invention
The present invention pertains to the following areas of technology:
PROSTHESIS (I.E., ARTIFICIAL BODY MEMBERS), PARTS THEREOF OR AIDS AND ACCESSORIES THEREFOR; implantable prosthesis for the spinal column such as vertebrae and spinal discs for example.
2. Description of the Prior Art:
U.S. Pat. No. 4,501,269 issued to Bagby on Feb. 26, 1985 discloses a basket-type of spinal implant.
U.S. Pat. No. 4,961,740 issued on Oct. 9, 1990 to Ray and U.S. Pat. No. issued on Oct. 8, 1991 also issued to Ray disclose a coil-type of spinal implant.
U.S. Pat. No. 5,015,247 issued on May 14, 1991 to Michelson discloses a threaded spinal implant.
In the early 1950's an operation was pioneered by Ralph B. Cloward, M.D. for the removal of ruptured cervical disc lesions and osteophytes by an anterior surgical approach. A herniated disc is a rupture or herniation of the intervertebral disc, especially between lumbar vertebrae. This usually causes pain in the affected side. An osteophyte is a bony excrescence or out-growth, which is usually branched in shape. The anterior surgical approach means that a transverse incision is made on the patient's throat just to the right of the wind pipe. The level of the lesions is identified before the operation either by injecting methylene blue dye into the disc under X-ray control the day before surgery or by a portable X-ray taken in the operating room with the needle inserted into the disc. Endotracheal general anaesthesia is used in most cases. The patient is placed in the supine position with the neck extended over a special neck rest. It is soft but firm and X-ray's can be taken through it. The head is turned to the left and secured to the table with an adhesive band across the forehead.
The location of the transverse incision is determined by the level of the lesion. The C5-6 disc lies beneath the cricoid cartilage and the adjacent disc one centimeter above or below. The various neck muscles and nerves are cut so that the anterior of the spinal cord is eventually exposed. A small rectangular retractor is placed around the disc area so that the surgeon has room within which to work. The disc that has the lesions is removed with a rongeur and a scalpel. The main objective of the Cloward procedure is to make at least one drill hole between the adjoining vertebrae to a sufficient depth but yet to prevent it from damaging any of the nerves contained within the spinal cord. After the drill hole has been completed, a complementary bone plug is removed from the patient's hip. The bone plug from the patient's hip is then positioned into the drill hole made in the pair of vertebrae. The hip bone plug will then fuse with the two vertebrae to create one vertebra that is fused together.
The guide used for the drill hole is usually placed slightly off center to the right of the midline regardless of lateralization of lesion so the drill will remove more bone on the right side. The bottom of the drill guard has pins which have to be hammered into the surface of the vertebrae to secure the drill guard for the operation. The guard pins on the drill guard do not harm the spinal cord because of the neck rest under the neck. Three drill tip sizes are available in diameters of 11.5 mm, 13.5 mm, and 15.5 mm, to accommodate the variation and the size of the vertebral bodies and the width of the disc spaces. The drill tips are interchangeable on a single drill shaft and are adjustable in length with the guard. A relief opening in the drill guard permits escape of bone dust and prevents the drill from binding. When drilling is complete, the guard and drill are removed and the drill hole immediately fill with a gel foam pad soaked in topical thrombin and packed with a padding.
The dowel is attached to the impactor tip. If the bone graft is too long or too large it can be tailored with a file to the appropriate size. Some surgeons are apprehensive that the dowel may be driven into the spinal canal damaging the spinal cord. This is a serious but avoidable complication. It can be prevented by using a dowel impactor tip larger then the drill hole. This will permit the dowel to be inserted only flush with the vertebra. It must then be recessed slightly with the smaller impactor two millimeters below the outer rim of the drill hole. Heavy pounding is unnecessary and should not be done. The distance between the dura and the inner end of the dowel can be determined by lowering the osteophyte elevator into the interspace lateral to the drill hole. The foot of the elevator is placed beneath the dowel and raised gently up and down.
With the wound closure, the two retractor blades are removed and the longus colli muscle is checked for bleeding points. Any bleeding from the outer margin of the drill hole or the guard pin holes can be arrested with bone wax.
Post operative pain from this operation is minimal and is controlled with mild analgesics. The patient is permitted to be up the day of the operation. Movements of neck are not restricted and no neck brace cast is required. A soft cervical collar is used for multiple level cases.
The patient is usually discharged from the hospital on the third or fourth day. X-rays are taken prior to discharge to determine the position of the bone graft or grafts and for comparison with subsequent follow-up films.
The parts which comprise the Cloward kit include: the skin retractor; cervical muscle retractor; blade retractor; cervical periosteal elevator; cervical retractor (large) with set of seven sharp blades; double hinged retractor handle; cervical retractor with seven blunt blades; rongeur; cervical vertebra spreader; depth gauge; the three drill tips of the three sizes previously mentioned; drill shaft with depth stop and drill guard; guard guide; drill guard cap; cervical hammer; cross bar handle; bone punch; tissue retractor; dowel cutter shaft; dowel cutter center pin; dowel holder; dowel handle and impactor set; and a curved cervical osteotome 4 mm in size.